Use of flow injection analysis coupled with Chemiluminescence detection for quality control of sulfonamides in pharmaceuticals

The coupling of flow injection manifolds with chemiluminescence detection (FIA-CL) is an interesting alternative in pharmaceutical quality control due to its advantages, such as, high sensitivity, easy implementation, simple instrumentation and low cost. Peroxyoxalate chemiluminescence (PO-CL) is an indirect CL in which a PO is oxidized in presence of H2O2 and imidazole as a catalyst, and an intermediate from the primary reaction transfers its energy to an energy-accepting fluorophore, which subsequently emits light. The use of POs presents some drawbacks arising from the of use organic solvents, as acetonitrile. We propose a FIA configuration based on the use of two injection valves for the introduction of both PO and derivatized analyte solutions in the flow system, avoiding the problems mentioned above, as neither special tubes nor special pumps are required. Furthermore, the use of micellar media (sodium dodecyl sulphate, SDS) as carrier and the addition of tetrahydrofurane (THF) in the PO solutions increase both the solubility and stability of POs, avoiding their rapid degradation in water. This CL-FIA system was applied to the determination of two sulfonamides for human and veterinary use: sulfadiazine (a sulfonamide mainly used in the treatment of urinary tract infections) and sulfamethoxazole (used mainly for bronchial affections) using bis[2,4,6-trichlorophenyl]oxalate (TCPO) as precursor and fluorescamine as fluorescent derivatizing agent. The optimization of instrumental and chemical variables was carried out by using experimental designs (Doehlert and 23 plus centered face star), separately for each sulfonamide. The method shows a LOQ of 379 µg l–1 (calibration range 126-2000 µg l–1) for sulfadiazine and has been successfully applied to the quantification of this sulfonamide in pills and ampoules, obtaining results according with those reported by the manufacturers. Further results will be presented for sulfamethoxazole. Acknowledgements: The National Institute of Agricultural and Food Research and Technology (INIA, Ministerio de Agricultura, Pesca y Alimentación, Project Ref. CAL03-087-C2-2) and EU founds (FEDER) supported this work. JJSC is grateful to the Fundación La Caixa and VPR to the Plan Propio of the University of Granada.